Grease composition for engine bearing

ABSTRACT

Disclosed is a grease composition for an engine bearing. The grease composition is a hybrid type grease composition which includes: a mixture of an ester-based base oil and a fluorine-based base oil as a base oil; and a mixture of a urea-based thickener and a fluorine-based thickener as a thickener. Accordingly, maximized effects in durability and heat resistance as the grease for an engine bearing may be obtained by optimally blending the base oils, the thickeners and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2013-0159028 filed on Dec. 19, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a grease composition for an engine bearing of a vehicle. Particularly, disclosed is a hybrid type grease composition which may include: a mixture of an ester-based base oil and a fluorine-based base oil as a base oil; and a mixture of a urea-based thickener and a fluorine-based thickener as a thickener. Accordingly, maximized effects in durability and heat resistance which are required for the grease for an engine bearing may be obtained by optimally blending the base oils, the thickeners and the like.

BACKGROUND

In the interior of an engine room of a vehicle, various types of electronic parts are attached. In pursuit of low fuel consumption, down-sizing, weight reduction, high performance and the like of vehicles, a high-speed bearing used in the electronic parts is essential. Consequently, substantial amount of heat is generated, and accordingly, the temperature at the bearing is elevated. Thus, the bearing that meets the requirements under above condition are under development, and grease used in the bearing has also been developed accordingly to reinforce durability and heat resistance, to thereby maintain the performance of parts.

In general, an engine belt is used to deliver the parts of engine output. In particular, the role of the bearing is essential for rotation. To withstand the load applied on the bearing and the friction of rotation when the chain is driving, grease is applied to the inside thereof to prevent noise of an engine room and tremor of a vehicle which may be caused by abnormal abrasion. In the engine bearing part which is exposed to heat generated from the engine and rotates at high speed, it is important to sustain durability characteristics. Accordingly, it is a core technology to simultaneously secure durability and heat resistance as well as lubricity of the grease.

Typically, the grease is composed of a base oil, a thickener, an additive and the like. A conventional base oil is a mineral oil which may include a synthetic hydrocarbon oil, an ester oil, and an ether oil. The thickener, as used herein, maintains grease in a semi-solid state and may be critical to change physical properties of grease. Therefore, it is important to select appropriate thickener. As the thickener, a metal soap thickener and a urea-based thickener are generally used. Grease for a vehicle generally uses a urea-based thickener due to its greater thermal stability and oxidation stability than the metal soap thickener.

The urea-based thickener may be prepared by reacting diisocyanate and amine, and the types of the urea-based thickener are also various. In the related art, a grease composition for vehicles has been developed. In the composition, alicyclic diurea which is obtained by reacting diphenylmethane-4, 4-diisocyanate (MDI) and cyclohexylamine is used as a thickener. However, a urea-based thickener in the related art may cause deterioration in friction characteristics, water resistance and the like when used in vehicle parts to which shearing and heat are simultaneously applied, particularly when used in in a grease composition for the vehicle engine.

Furthermore, in the related art, another type of grease composition for a bearing has been reported. The grease composition includes a fluorine-based base oil and a polytetrafluoro ethylene (PTFE) thickener. However, the grease composition composed of the fluorine-based base oil and the PTFE thickener may have adverse effects in noise characteristics of the bearing due to the content of PTFE. In addition, the lubricity thereof may deteriorate, and the range of selecting an additive may be narrowed, so that high performance thereof may not be obtained.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present invention provides technical solutions to the above-described technical difficulties in the related art. In one aspect, the present invention provides a grease composition for an engine bearing, which may simultaneously improve durability and heat resistance as well as lubrication.

In an exemplary embodiment, the grease composition for an engine bearing may include: an ester-based base oil in an amount of about 50 to 70 wt %; a fluorine-based base oil in an amount of about 18 to 30 wt %; a urea-based thickener in an amount of about 8 to 15 wt %; a fluorine-based thickener in an amount of about 1 to 10 wt %; and an additive in an amount of about 1 to 10 wt %. It is understood that wt % of grease components as disclosed herein are based on total weight of the grease composition, unless otherwise indicated.

Other aspects and preferred embodiments of the invention are discussed infra.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

The present invention relates to a novel grease composition for an engine bearing, which includes a base oil, a thickener, and an additive. Particularly, a hybrid type grease composition which may include a mixture of an ester-based base oil and a fluorine-based base oil as the base oil and a mixture of a urea-based thickener and a fluorine-based thickener as the thickener is disclosed. Each component constituting the grease composition according to the present invention will be specifically described as follows.

In an exemplary embodiment, the grease composition of the present invention may include: a mixture of an ester-based base oil having improved lubricity and a fluorine-based base oil having improved heat resistance as the base oil. The base oil may have a kinematic viscosity of about 90 to 150 cSt at 40° C., or particularly of about 100 to 110 cSt. The ester-based base oil and the fluorine-based base oil, as used as a base oil herein, may be components generally used in the art for preparing grease, the present disclosure has no particular limitation in selecting components of the ester-based base oil and the fluorine-based base oil. As disclosed herein, lubricity, durability and heat resistance which are required properties for the grease for an engine bearing may be simultaneously improved by preparing these base oils at an appropriate ratio of the components and using the resulting mixture.

The ester-based base oil, as used herein, may be used as a base oil in the present invention. The ester-based base oil includes an ester group (—COO—) in a molecular structure thereof. The ester-based base oil may be, but not limited to, diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate and ditridecyl phthalate; aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate and tetraoctyl pyromellitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate and pentaerythritol pelargonate; carbonate ester oils and the like.

The ester-based base oil may be included in a range from about 50 to about 70 wt %, or particularly in a range from about 55 to about 60 wt %, based on the total weight of the grease composition. When the content of the ester-based base oil included in the grease composition is less than about 50 wt %, ester-based oil and the fluorine-based oil may be separated. When the content is greater than about 70 wt %, the content of the fluorine oil accordingly decreases, so that heat resistance may be reduced.

The fluorine-based base oil, as used herein, may also be a base oil. The fluorine-based base oil may include one or more fluorine atoms in a molecular structure thereof. The fluorine-based base oil may be, but not limited to, a fluorine-based polyether oils such as perfluoroalkyl polyether (PEPE), and the like. For example, the perfluoroalkyl polyether represented in the following Formula 1 may be used as a fluorine-based base oil.

C_(x)F_(2x+1)-[O—CF(CF₃)—CF₂]_(n)-(O—CF₂)_(m)—O—C_(y)F_(2y+1)   Formula 1

wherein, each of x and y is 1, 2 or 3, n is 40 to 20, m is 0.5 to 1, and n/m >40.

The fluorine-based base oil may be included in a range from about 18 to about 30 wt %, or particularly in a range from about 20 to about 25 wt %, based on the total weight of the grease composition. When the content of the fluorine-based base oil included in the grease composition is less than about 15 wt %, friction characteristics may deteriorate. When the content is greater than about 30 wt %, the fluorine base oil may be separated from the grease and evaporated.

In addition, the grease composition of the present invention may include a mixture of a urea-based thickener and a fluorine-based thickener as a thickener. When the fluorine-based thickener is used as a sole thickener, the grease may be prepared in the form of a paste, so that heat resistance and abrasion resistance as the thickener may deteriorate. Further, the application to a substantially high speed and substantially high temperature bearing may not be appropriate. Further, when the urea-based thickener is used as a sole thickener, the grease may be prepared by a C—H bond with the ester-based base oil and a hydrogen bond with the fluorine-based base oil. In particular, physical properties, such as friction and heat resistance, of the grease composition may deteriorate compared to the grease composition in which a mixture of a urea-based thickener and a fluorine-based thickener is used.

The urea-based thickener and the fluorine-based thickener, which may be used as a thickener as disclosed herein, may be components generally used in the art for preparing a grease composition, and the present invention does not have any particular limitation in selecting components for the thickener. In the exemplary embodiments of the present invention, the thickener may be prepared by mixing the components at an appropriate ratio, to simultaneously satisfy lubricity and durability required for the grease for an engine bearing in a vehicle.

The urea-based thickener, as used herein as the thickener component, may be obtained by reacting a diisocyanate component and an amine component. Examples of the diisocyanate component may be, but not limited to, aliphatic diisocyanates or aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate or hexane diisocyanate. In an exemplary embodiment, the diisocyanate component may be aromatic diisocyanates. Furthermore, the amine component may be, but not limited to, a monoamine or diamine compound. Examples of the monoamine compound may be, but not limited to, aliphatic amines such as hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine or oleylamine and aromatic amines such as aniline and p-toluidine. Examples of the diamine compound may be, but not limited to, aliphatic diamines or aromatic diamines such as ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine and diaminodipheneylmethane.

The urea-based thickener may be included in a range from about 8 to about 15 wt %, or particularly in a range from about 10 to about 15 wt %, based on the total weight of the grease composition. When the content of the urea-based thickener included in the grease composition is less than about 5 wt %, the capability of maintaining the base oil may be insufficient, and a substantial amount of the oil component may be separated at a time. Consequently at the initial period of rotation, and grease may leak, thus decreasing the durability life-span of the bearing. When the content is greater than about 20 wt %, the amount of the base oil may decrease accordingly, such that oil supplement may not be sufficient, and lubricity may lack in the initial period. Consequently, the durability life-span of the bearing may be shortened.

The fluorine-based thickener, as used herein as another thickener component, may include one or more fluorine atoms in a molecular structure thereof, and examples thereof may be, but not limited to, polytetrafluoroethylene (PTFE) and the like.

The fluorine-based thickener may be included in a range from about 1 to about 10 wt %, or particularly in a range from about 5 to about 10 wt %, based on the total weight of the grease composition. When the content of the fluorine-based thickener included in the grease composition is less than about 1 wt %, sufficient durability may be obtained since all the fluorine base oils are not reacted. When the content is greater than about 15 wt %, since the fluorine-based thickener itself may serve as a solid lubricant, bearing noise and reduced durability may be caused.

Further, the grease composition, as disclosed herein, may contain a publicly known additive for grease, if necessary, in addition to the base oil and the thickener. Examples of the additive may be, but not limited to: an antioxidant such as an organic zinc compound, an amine-based compound and a phenol-based compound; a metal deactivator such as benzotriazole; a viscosity index improver such as a polymethacrylate and polystyrene; a solid lubricant such as molybdenum disulfide (MoS₂) and graphite; a corrosion inhibitor such as metal sulfonate and polyvalent alcohol ester; a friction modifier such as organic molybdenum compound; an oiliness agent such as ester and alcohol; an anti-wear agent such as a phosphorus compound; and the like. In particular, at least one or more of the aforementioned-additives may be added.

In the exemplary embodiments of the present invention, zinc dithiophosphate (ZnDTP) may be added in a range from about 1 to about 2 wt %, based on the total weight of the grease composition to obtaining a maximized effect of abrasion resistance characteristics of the grease.

In addition, a polymer may be added to the grease composition as the additive to increase adhesiveness. The polymer may be, but not limited to, polyisobutylene. Further, a surfactant may be added to the grease composition as a structure stabilizer to improve stability of the structure by dispersing the thickener sufficiently.

The aforementioned additives may be added independently (e.g., individually) in a range from about 1 to about 2 wt %, based on the total weight of the grease composition. Further, the total combined amount of these additives may be maintained in a range from about 1 to about 10 wt % in the grease composition. When the combined amount of these additives is greater than about 10 wt %, the effect according to an increase in the content may not be obtained, and the content of other components may decrease accordingly. Additionally, these additives in the grease may be aggregated, so that deterioration in the grease properties may be caused such as an increase in torque.

The present invention as described above will be described in more detail with reference to the following Examples, but the present disclosure is not limited to the following Examples.

EXAMPLES

The following examples illustrate the invention and are not intended to limit the same.

Example 1 Preparation of Grease Composition

The composition components are blended in a specific content ratio as described in Table 1, and the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 11 are prepared.

Reagents and Materials

1) Ester-based base oil: manufactured by HATCO Corp.

2) PFPE base oil: Perfluoroalkyl polyether, manufactured by Solvay, Inc.

3) Ether-based base oil: manufactured by Matsumura Oil Co., Ltd.

4) Urea-based thickener: Aliphatic urea

5) PTFE thickener: Polytetrafluoroethylene, manufactured by DuPont, Inc.

6) ZnDTP: Zinc dithiophosphate

7) MoS₂: Molybdenum disulfide

TABLE 1 Grease Composition (wt %) Base oil Kine- matic vis- Clas- Ester- Ether- cosity^(a)) Thickener Additive sification based PFPE based (cSt) Urea PTFE ZnDTP MoS₂ Example 1 58 20 — 102 15 5 2 — 2 58 20 — 102 10 10 2 — 3 54 24 — 102 10 10 2 — Com- 1 46 32 — 102 10 10 2 — parative 2 62 16 — 102 10 10 2 — Example 3 58 20 — 102 17 3 2 — 4 58 20 — 102 5 15 — 2 5 60 20 — 102 10 10 — — 6 60 20 — 102 10 10 2.5 — 7 57.5 20 — 102 20 — 2 — 8 58 20 — 102 — 20 2 — 9 80 — — 102 20 — — — 10 — 80 — 102 — 20 — — 11 — — 80 102 20 — — — ^(a))Kinematic viscosity: Kinematic viscosity of base oil at 40° C.

Example 2 Evaluation

Properties of each grease composition prepared in Examples 1 to 3 and Comparative Examples 1 to 11 were tested in accordance with a publicly known performance test method, and the results are shown in Table 2.

Performance Test Method

1) Base oil separation: The base oil is left to stand at normal temperature, and then it is observed whether the base oil separation phenomenon occurred with the naked eyes.

2) Evaporation amount: The evaporation amount of the base oil is measured at a temperature of about 160° C. in accordance with the standard ASTM D 972 test method.

3) Amount of 4-BALL abraded: The abrasion amount is measured by evaluation with the standard ASTM D 2266.

4) Bearing durability: The bearing durability is measured by using a bearing outer ring rotation rig.

5) Evaluation of bearing noise: The bearing noise is evaluated by Anderon meter manufactured from SUGAWARA, JAPAN.

TABLE 2 Evap- oration Abrasion Bearing Evaluation Clas- Separation amount amount durability of bearing sification of base oil (wt %) (mm) (hr) noise Example 1 Good 0.08 0.39 — 2 2 Good 0.08 0.40 — 2 3 Good 0.08 0.39 667 2 Com- 1 Separation 0.12 0.51 — 2 parative 2 Good 0.09 0.58 — 2 Example 3 Good 0.08 0.44 337 2 4 Good 0.08 0.75 — 4 5 Good 0.08 Unable Modification 1 to be of measured thickener 6 Good 0.08 0.41 — 5 7 Good 0.10 0.42 — — 8 Good 0.21 0.56 — 4 9 Good 0.09 0.56 317 — 10 Good 0.08 0.43 556 3 11 Good 0.10 0.74 180 —

According to the result of Table 2, the hybrid type grease compositions of Examples 1 to 3 in which the mixture of ester-based/fluorine-based base oil and the urea-based/fluorine-based thickener mixture are included in a constant content ratio may be more stably stored without separation of the base oil, and have improved heat resistance and durability. In addition, for Examples 1 to 3, noise evaluations are satisfactory. Further, the grease compositions of Comparative Examples 7 to 11 including the base oil and/or the thickener as a single component may have adverse characteristics in heat resistance or durability.

Although the hybrid type grease composition in which the ester-based/fluorine-based base oils are together included, a base oil separation may occur in the grease composition of

Comparative Example 1 in which the content of the fluorine-based base oil is included greater than the predetermined amount. In Comparative Example 2 in which the content of the ester-based base oil is included greater than the predetermined amount, durability may be reduced.

Furthermore, in the hybrid type grease compositions of Comparative Examples 3 and 4 which include the urea-based/fluorine-based thickener mixture, durability thereof may be reduced when the content of the urea-based or fluorine-based thickener are included greater than the predetermined amount of the present invention. In addition, the grease composition of Comparative Example 4 which includes molybdenum disulfide (MoS₂) as an additive instead of zinc dithiophosphate (ZnDTP) may have significantly reduced durability.

Moreover, in the test results of Comparative Examples 5 and 6, the effects of the additive in the hybrid type grease composition in which the ester-based/fluorine-based base oil mixture and the urea-based/fluorine-based thickener mixture were included in a predetermined content ratio are compared. In the grease composition of Comparative Example 5 in which no additive was included, modification of the thickener is caused. Further, in the grease composition of Comparative Example 6 in which zinc dithiophosphate (ZnDTP) is included greater than the predetermined amount, noise and vibration phenomenon is observed.

The typical grease composition may include a base oil, a thickener and an additive. Moreover, according to various exemplary embodiments of the present invention, determining the composition components and the component ratio may be critical to provide the maximum performance of the parts where the grease composition is applied.

The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. 

What is claimed is:
 1. A grease composition for an engine bearing, comprising: an ester-based base oil; a urea-based thickener; and an additive, wherein the grease composition comprises the ester-based base oil in an amount of about 50 to 70 wt %; a fluorine-based base oil in an amount of about 18 to 30 wt %; the urea-based thickener in an amount of about 8 to 15 wt % of; a fluorine-based thickener in an amount of about 1 to 10 wt %; and the additive in an amount of about 1 to 10 wt %, based on the total weight of the grease composition.
 2. The grease composition for an engine bearing of claim 1, wherein the additive includes zinc dithiophosphate (ZnDTP) in an amount of about 1 to 2 wt % of, based on the total weight of the grease composition.
 3. The grease composition for an engine bearing of claim 1, wherein the base oil composed of the ester-based base oil and the fluorine-based base oil has a kinematic viscosity of in a range from about 90 to about 150 cSt at a temperature of about 40° C.
 4. The grease composition for an engine bearing of claim 1, wherein the fluorine-based base oil is a fluorine-based polyether oil.
 5. The grease composition for an engine bearing of claim 1, wherein the fluorine-based thickener is polytetrafluoroethylene (PTFE). 